N-acylhomocysteine thiolactone stabilizers for photographic silver halide emulsions



Unite States This invention relates to photographic materials and to methods of preparing them. More particularly, this invention relates to light-sensitive silver halide emulsions cqntaining as a stabilizing and antifogging agent an N- acyl DL-homocysteine thiolactone.

It is well known in the photographic art that lightsensitive emulsions such as gelatino-silver halide emulsions have a tendency to fog. Fog is usually caused by a prolonger ripening of the emulsion, by prolonged storage especially at elevated temperatures and humidity and by prolonged development. To overcome this undesira ble property, it has been the practice in this art to add certain chemical compounds to the emulsions to increase their stability and to reduce their tendency to fog. However, the stabilizing and antifogging compounds heretofore used in this art have the disadvantage that upon addition to the emulsion they cause a loss of speed and/ or contrast of the emulsion.

It is, accordingly, an object of this invention to produce Ea light-sensitive emulsion which is fast, stable, has a :reduced tendency to fog and has good contrast.

A further object of this invention resides in a lightsensitive emulsion which contains a compound which stabilizes the emulsion against fogging and at the same time does not materially reduce the speed and/or the contrast of the emulsion.

I have discovered that N-acyl DL-homocysteine thiolactones when added to a light-sensitive silver halide emulsion, stabilize and inhibit the fogging of the emulsion. The N-acyl DL-homocysteine thiolactones, the use of which is contemplated herein, may be represented by the following formula:

COR

3,Gfi8,l00 Patented Dec. 11, 1962 NH O O C3H7 N-butyryl DL-homocysteine thiolactone to the emulsion at any stage during its process of prowherein R is a low alkyl radical; for example, methyl,

/S s u 112 I NH-C O CH:

N-acetyl DL-homocysteine thiolactone N-proplonyl DL-homocysteine thlolactone duction. Thus, they may be added as a ripening final or as a coating final." When added as a ripening final," they are added during the ripening or sensitivity increasing stage of the emulsion-making process. Such addition may be made before, during or after the addi-' tion of the soluble silver salt to the soluble halide in the presence of a suitable colloid such as gelatin, polyvinyl alcohol, solubilized casein or albumin which may be used' as the carrier material. When added as a coating final, the antifogging agent of my invention is added to the emulsion just prior to coating it on a suitable support such as glass, paper or film at a time when the emulsion has nearly attained its maximum sensitivity. In some instances, it is advantageous to apply the antifogging and stabilizing compounds of my invention in a separate layer such as an under coating layer or in an anti-abrasion gelatin surface. Sometimes it is desirable to incorporate the compounds in one or all processing baths; for instance, in the developer solution or in the pre-bath which is used prior to development.

When used as a ripening final, the antifoggants of my invention are preferably added to the emulsion in an amount ranging from 0.1 milligram to 60 milligrams per 0.6 mol of silver halide; and when used as a coating final, they are preferably added in an amount ranging from 10 milligrams to 300 milligrams per 0.6 mol of silver halide. The optimum amount to be added depends primarily on the type of emulsion and should be determined individually in each case.

The stabilizers and antifoggants of my invention may also be used in combination with known antifoggants and stabilizers; the antifoggants of my invention can also be used in combination with sensitizers such as sulfur, metal and reduction sensitizers as well as with speed-increasing agents and accelerators such as the reaction products of long-chain alcohols and ethylene oxide (see United States Patent 1,907,578) and their derivatives.

The novel antifoggants of my invention may be used with various types of photographic emulsions such as non-sensitized orthochromatic, panchromatic and X-ray emulsions, paper emulsions and color emulsions.

The following specific examples are given as an illustration of the manner in which the antifoggants of my invention can be used. It is to be understood, however, that these examples are given by way of illustration and not by way of limitation.

PREPARATION A mixture of 12.25 grams of DL-homocysteine thiolactone hydroiodide and 8.35 grams of silver acetate dispersed in 500 milliliters of glacial acetic acid was stirred for 30 minutes at room temperature. The silver iodide which was formed in this reaction was removed by filtration. Ten millilitersof freshly distilled acetic anhydride was added to the filtrate and the mixture allowed to stand for 2 hours. The acetic acid was distilled off in vacuum,

and the residue dried over sodium hydroxide in a vacuum desiccator. The residue was recrystallized from toluene and yielded a product having a melting point of 110 C.

Example I A silver halide emulsion in gelatin containing 2 percent silver iodide and 98 percent silver bromide was prepared in a conventional manner and brought up to its maximum light sensitivity. It was then readied for coating by adding finals such as sensitizing dyes and hardening agents. A 0.1 percent solution of N-acetyl DL-homocysteine thiolactone prepared as described above was added in varying amounts to samples of the emulsion as an antifoggant and stabilizer. Each emulsion sample contained about 0.6 mol of silver halide. The so prepared emulsion samples were coated on a suitable cellulose ester base and dried. Samples of these film coatings were then exposed in a Type IIB Sensitometer and developed in a developer of the following composition:

' Grams Metol (p-methylaminophenol sulfate) 1.5 Sodium sulfite (anhydrous) 45.0 Sodium bisulfite 1.0 Hydroquinone 3.0 Sodium carbonate (mcnohydrate) 6.0 Potassium bromide 0.8

Water to make 1.0 liter.

The developed samples were short-stopped, fixed and washed and dried. The results obtained were as follows:

Fog at Oven fog Quantity of compound used Relative 12 min. at 6 min.

speed developdevelopment ment Example II The procedure followed was identical to Example I except that in place of N-acetyl DL-homocysteine thiolactone the compound used was N-propionyl DL-homocysteine thioiactone prepared in an analogous manner except that propionic anhydride was used in place of acetic anhydride.

The results obtained were substantially identical with those of Example I.

Example III The procedure followed was identical to Example I but in place of used the compound N-butyryl DL-homocysteine thiolac tone which had been prepared by using butyric anhydride in place of acetic anhydride.

The results obtained were very similar to those of Example I.

Example IV Several examples of a conventional film were exposed in a Type IIB Sensitometer and then divided into two groups. One group of samples was developed for twelve minutes at 68 F. in a standard metol hydroquinone developer as described in Example I. The second group of samples was developed for the same length of time and at the same temperature as the first group in a metol hydroquinone developer which had been prepared by adding to the developer described in Example I 10 mgs. of N-acetyl DL-homocysteine thiolactone per liter of developer. It was found that both sets of samples had the same relative speed of 100. However, the samples developed in the control developer showed a fog of .30 whereas the strips which had been developed in the presence of the antifoggant showed a fog of 0.20.

N-acetyl DL-homocysteine thiolactone was 4 Example V One kilo of a silver halide emulsion in gelatin contain ing 4 percent silver iodide and 96 percent silver bromide was coated on film base in a manner known to the art. After the coating was performed, an aqueous gelatin solution containing 20 grams of gelatin per liter and 1.2 grams of the N-acetyl DL-homocysteine thiolactone of Example I was coated thereon as an antiabrasion layer. After drying, film samples were exposed and processed as described in Example I. The samples described exhibited a relative speed of 100 with a fog of .12 as compared with a type coating of the same emulsion having an antiabrasion layer similar to that described above but lacking the antifogging additive and having a speed of 100 and a fog of .20.

Modifications of the invention will occur to persons skilled in the art. I do not intend to be limited in the patent granted except as necessitated by the appended claims.

I claim:

I. A light-sensitive silver halide emulsion containing in a stabilizing amount an antifoggant compound having the following general chemical formula:

l IIIH COR wherein R is a lower alkyl group of from 1 to 3 carbon.

atoms.

2. A light-sensitive silver halide emulsion as recited in claim 1 wherein the antifogging and stabilizing compound is N-acetyl DL-homocysteine thiolactone.

3. A light-sensitive silver halide emulsion as recited in claim 1 wherein the antifoggin'g and stabilizing com- I pound is N-propionyl DL-cysteine thiolactone.

4. A light-sensitive silver halide emulsion as recited in claim 1 wherein the antifogging and stabilizing compound I is present in the emulsion in the ratio of 0.1 to 300 milligrams per 0.6 mol of silver halide.

5. A light-sensitive silver halide emulsion as recited in claim 1 containing a sensitizing dye.

6. A light-sensitive silver halide emulsion as recited in claim 1 containing the reaction product of a long chain alcohol and an ethylene oxide as an accelerator.

7. A light-sensitive photographic element comprising a base and a coating of gelatino silver halide emulsion; thereon said emulsion containing as an antifogging andstabilizing agent a compound having the following general formula:

l con fogging and stabilizing agent a compound selected from the group having the following general structure:

I NH

l COR wherein R is a member selected from the group consisting of methyl, ethyl and propyl.

13. A process according to claim 12 wherein said corn i pound is N-aectyl DL-homocysteine thiolactone.

14. A process of forming a photographic emulsion having a reduced tendency to fog which comprises forming the emulsion, ripening the emulsion and during said ripening adding thereto a compound having the following general formula:

COR

wherein R is an alkyl group of from 1 to 3 carbon atoms.

15. A process according to claim 14 wherein said compound is N-acetyl DL-homocysteine thiolactone.

16. The process of minimizing and preventing fog on light-sensitive silver halide materials comprising a base having a light-sensitive silver halide emulsion thereon which comprises exposing the emulsion and developing the exposed emulsion in the presence of an antifogging amount of a compound having the following general formula:

COR

wherein R represents a member selected from the group consisting of methyl, ethyl and propyl radicals.

17. A process according to claim 16 wherein said antijoggant is N-acetyl DL-homocysteine thiolactone.

18. A process according to claim 16 wherein said anti foggant is N-propionyl DL-homocysteine thiolactone.

19. A photographic developer solution comprising an organic developing agent, an alkali, an alkali metal sulfite, an alkali metal bromide and as an antifoggant, in an antifogging amount, a compound having the following general formula:

S Cr (i /gs COR wherein R represents an alkyl group having one to three carbon atoms.

20. A photograph developer solution according to claim 19 wherein said compound is N-acetyl DL-homocysteine thiolactone.

References Cited in the file of this patent UNITED STATES PATENTS 2,824,001 Allen et a1 Feb. 18, 1958 2,870,015 Allen et al. Jan. 20, 1959 2,939,789 Dersch et al. June 7, 1960 OTHER REFERENCES Glafkides: Photographic Chemistry, vol. I, Fountain Press, London, 1958, pages 374-75.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,068,100 December 11, 1962 Fritz Dersch It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 19, for "prolonger" read prolonged column 2, llne 53, for "l,907,578" read 1,970,578

Signed and sealed this 3rd day of September 1963 (SEAL) Attest:

ERNEST w. SWIDER DAVID LADD Attesting Officer Commissioner of Patents 

19. A PHOTOGRAPHIC DEVELOPER SOLUTION COMPRISING AN ORGANIC DEVELOPIN G AGENT, AN ALKALI, AN ALKALI METAL SULFITE, AN ALKALI METAL BROMIDE AND AS AN ANTIFOGGANT, IN AN ANTIFOGGING AMOUNT, A COMPOUND HAVING THE FOLLOWING GENERAL FORMULA: 